Charles stands in front of the Willamette meteorite, the largest found in the United States, housed in the Museum's Hall of the Universe.

Dr. Charles Liu, an astrophysicist at the American Museum of Natural History, clearly takes great delight in his work. As he explains the intricacies of what happens when galaxies collide, a smile spreads across his face. "Astronomy is just really fun," he says. In addition to his research, Charles shares his passion for astronomy by giving public lectures, teaching university–level astronomy classes, writing popular science books and articles, and creating courses for teachers.

Charles grew up in Ithaca, New York, where his father was a professor in the school of agriculture at Cornell. By the time he was in junior high school, even though he was involved in music, theater, and a number of other interests, he already knew he was going to be a scientist. Charles says, "There wasn't any particular event or epiphany; I just slowly came to realize that science was the right career for me." As a sophomore physics major at Harvard, Charles decided to focus on astronomy because he was eager to get involved in research as quickly as possible. "There were fewer students and more faculty in astronomy," he recalls, "so there were more opportunities for undergraduates to contribute." Unlike physics, which has been studied thoroughly for centuries, astrophysics is still a relatively wide–open field for young researchers. "There's a lot of sky, a lot of stars, and there's still so much we haven't observed," Charles points out. There are also many ways of studying the same patch of sky by observing at different wavelengths, and new technologies are constantly bringing fundamental new discoveries, making it an exciting time to do astrophysics research.

When Charles was weighing graduate schools, he decided he had had "too much exposure to non–sunny climates." So one place he considered was the University of Arizona, in Tucson, which is both home to a leading astrophysics research institution and an extraordinarily sunny place. Apart from California, Charles had never been west of the Mississippi, and he was unprepared for Arizona's stunning landscape. He recalls driving through the Sonoran Desert for the first time from Tucson to Kitt Peak National Observatory and being bowled over by the forests of towering saguaro cactuses. As he headed up Kitt Peak itself, he pulled off the road and looked out over the mountainside at the desert landscape, without a cloud in the sky, and a hawk circling below. "It was so beautiful," he says, "by the time I got back in the car I was hooked on being an observational astronomer."

The University of Arizona proved to be an excellent choice for Charles. "It was just a great, great place," recalls Charles. "The research, the environment, the faculty—they were all fantastic." At Arizona, Charles became interested in the star formation that occurs when galaxies collide. Galaxies are, in fact, colliding all the time. Says Charles, "There are a hundred billion stars coming this way, and a hundred billion stars coming that way, and when the galaxies collide they form a hundred million more."